Editing On-board diagnostics (section)

===Mode of operation/OBD services===

Here is a basic introduction to the OBD [[communication protocol]] according to ISO 15031. In SAE J1979 these "modes" were renamed to "services", starting in 2003.

* '''Service / Mode <code>$01</code>''' shows current sensor live data from PIDs ("Parameter IDs"). See [[OBD-II PIDs#Service_01]] for an extensive list.
* '''Service / Mode <code>$02</code>''' makes Freeze Frame data accessible via the same PIDs.<ref>{{Cite web|last=Miller|first=Tim|date=2019-06-07|title=How Can I Read OBD2 Freeze Frame Data?|url=https://obdplanet.com/obd2-freeze-frame-data/|access-date=2020-07-22|website=OBD Planet|language=en-US}}</ref> See [[OBD-II PIDs#Service_02]] for a list.
* '''Service / Mode <code>$03</code>''' lists the emission-related "confirmed" diagnostic trouble codes stored. It either displays numeric, 4 digit codes identifying the faults or maps them to a letter (P, B, U, C) plus 4 digits. See [[#OBD-II_diagnostic_trouble_codes]].
* '''Service / Mode <code>$04</code>''' is used to clear emission-related diagnostic information. This includes clearing the stored pending/confirmed DTCs and Freeze Frame data.<ref>{{Cite web|last=Miller|first=Tim|date=2018-02-28|title=How To Read OBD2 Freeze Frame Data|url=https://www.obdadvisor.com/freeze-frame/|access-date=2021-11-23|website=OBD Advisor|language=en-US}}</ref>
* '''Service / Mode <code>$05</code>''' displays the oxygen sensor monitor screen and the test results gathered about the oxygen sensor. There are ten numbers available for diagnostics:
** <code>$01</code> Rich-to-Lean O2 sensor threshold voltage
** <code>$02</code> Lean-to-Rich O2 sensor threshold voltage
** <code>$03</code> Low sensor voltage threshold for switch time measurement
** <code>$04</code> High sensor voltage threshold for switch time measurement
** <code>$05</code> Rich-to-Lean switch time in ms
** <code>$06</code> Lean-to Rich switch time in ms
** <code>$07</code> Minimum voltage for test
** <code>$08</code> Maximum voltage for test
** <code>$09</code> Time between voltage transitions in ms
** See [[OBD-II PIDs#Service_05]] for a list.
* '''Service / Mode <code>$06</code>''' is a Request for On-Board Monitoring Test Results for Continuously and Non-Continuously Monitored System. There are typically a minimum value, a maximum value, and a current value for each non-continuous monitor.
* '''Service / Mode <code>$07</code>''' is a Request for emission-related diagnostic trouble codes detected during current or last completed driving cycle. It enables the external test equipment to obtain "pending" diagnostic trouble codes detected during current or last completed driving cycle for emission-related components/systems. This is used by service technicians after a vehicle repair, and after clearing diagnostic information to see test results after a single driving cycle to determine if the repair has fixed the problem. See [[#OBD-II_diagnostic_trouble_codes]].
* '''Service / Mode <code>$08</code>''' could enable the off-board test device to control the operation of an on-board system, test, or component.
* '''Service / Mode <code>$09</code>''' is used to retrieve vehicle information. Among others, the following information is available:
** VIN ([[Vehicle identification number|Vehicle Identification Number]]): Vehicle ID
** CALID (Calibration Identification): ID for the software installed on the ECU
** CVN (Calibration Verification Number): Number used to verify the integrity of the vehicle software. The manufacturer is responsible for determining the method of calculating CVN(s), e.g. using checksum.
** In-use performance counters
*** Petrol engine : Catalyst, Primary oxygen sensor, Evaporating system, EGR system, VVT system, Secondary air system, and Secondary oxygen sensor
*** Diesel engine : NMHC catalyst, NOx reduction catalyst, NOx absorber Particulate matter filter, Exhaust gas sensor, EGR system, VVT system, Boost pressure control, Fuel system.
** See [[OBD-II PIDs#Service_09]] for an extensive list.
* '''Service / Mode <code>$0A</code>''' lists emission-related "permanent" diagnostic trouble codes stored. As per CARB, any diagnostic trouble codes that is commanding MIL on and stored into non-volatile memory shall be logged as a permanent fault code. See [[#OBD-II_diagnostic_trouble_codes]].